Adam et al.: Dynamics of Thunnus obesus and T albacares in Hawaii's pelagic fisheries 



227 



time and become vulnerable in the fishery. More recently, 

 archival tagging on drifting FADs in the eastern Pacific 

 Ocean have shown that bigeye tuna remain resident in the 

 general area of release for at least about an year (Schae- 

 fer and Fuller, 2002). In our study virtually all (99.4%) of 

 bigeye tuna recoveries were made within the model area. 

 These observations suggest some degree of regional fidelity 

 in the exploited phase (medium size) of bigeye tuna and a 

 low level of mixing with the central western Pacific region 

 for these immature size classes. However, it appears that 

 larger size bigeye tuna are not resident in Hawaiian wa- 

 ters because spawning condition adults do not recruit to 

 the local longline or handline fisheries. It is likely that as 

 these fish mature they move to warmer waters to the south 

 of Hawaii where bigeye tuna spawning is known to occur 

 (Nikaido et al, 1991). 



The extent of catch interaction between the Cross Sea- 

 mount fishery and the domestic inshore and longline fish- 

 eries does not appear to be of great management concern at 

 current levels of exploitation. However, given that current 

 exploitation rates are considered moderate (10-30%) and 

 the seamount aggregations are highly vulnerable to low 

 cost gear types, it was recommended that further increases 

 in fishing effort for yellowfin and bigeye tuna be monitored 

 at Cross Seamount. This note of caution is reinforced by the 

 increased concern over recent bigeye and yellowfin tuna 

 stock assessments from the western and central Pacific 

 (Hampton and Fournier, [2001]; Hampton and Fournier'-). 

 These assessments suggest declining adult biomass, declin- 

 ing recruitment, and greatly increased fishing mortality on 

 juveniles in the equatorial region, which is probably the 

 main source of recruitment to the Cross Seamount and 

 Hawaii-based fisheries. 



Additional strategic tagging experiments involving the 

 release of tuna should represent the full geographic and 

 size range landed in the fisheries to adequately refine 

 our estimates of fishery interaction and transfer rates. 

 Comparative studies of yellowfin and bigeye tuna using 

 electronic tags would also help to understand differences 

 in how the two species partition their habitat. However, the 

 current size-based estimates of natural and fishing mortal- 

 ity rates, together with transfer rates and other ancillary 

 information, still remain useful to conduct a yield-per-re- 

 cruit analysis to investigate various scenarios arising from 

 an increase or decrease in fishing effort and its effects on 

 the fishery components. The results of this analysis will 

 also be useful in refining stock assessment models that are 

 currently being developed for the species. 



Acknowledgments 



The research was funded under Cooperative Agreement 

 No. NA67RJ0154 from National Oceanographic Atmo- 

 spheric Administration and administered by the Pelagic 

 Fisheries Research Program, Joint Institute of Marine and 

 Atmospheric Research of the University of Hawaii. We are 

 grateful to Pierre Kleiber for his advice in the data analy- 

 sis. Comments from two anonymous reviewers greatly 

 improved the manuscript. 



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